Ireland’s leading media owner and one of the country’s richest men has been accused of gagging free speech and even parliamentary privilege over his attempt to silence members of the Dáil raising issues about his finances.

Denis O’Brien, the major shareholder in Ireland’s Independent News and Media Group, won an injunction that his lawyers argue prevents Irish broadcaster RTÉ from reporting a speech by a leftwing Dáil deputy who raised questions about the billionaire’s relationship with the state-owned bank, the IBRC.

The IBRC is the offspring of the now defunct and disgraced Anglo Irish Bank, the financial institution that almost bankrupted the state through reckless lending to some of the republic’s wealthiest investors.

Independent TD Catherine Murphy used Dáil parliamentary privilege to question whether O’Brien enjoyed a favourable interest rate of 1.25% with the state-owned bank, when the IBRC should have been charging him up to 7.5%.

A number of broadcasting organisations received threatening letters from O’Brien’s lawyers and did not report Murphy’s remarks in the Dáil.

Murphy, TD for Kildare North, said the favourable interest enabled O’Brien to “pay off his own loans in his own time at low interest rates”. The deal was to enable O’Brien to purchase the Siteserv company, a utility firm that installs controversial water meters across the republic.

O’Brien last week applied for a injunction to restrain broadcasters reporting about his deal with IBRC on the grounds that it breached his privacy rights and would cause him incalculable commercial damage.

IBRC, which brought a separate but related application before the court, supported O’Brien.

RTÉ opposed the injunction on grounds including the right to freedom of expression and public interest. It also argued the courts should be slow to interfere with legitimate journalistic judgment.

The broadcaster argued O’Brien’s suggestion that the report could have been run without naming him would result in a boring and sterile story.

Padraig Reidy, editor of the Little Atoms website and a commentator on Irish media, condemned the use of injunctions that applied to the Irish parliament.

“The fear of reporting even privileged Dáil speech shows how dangerous the extent of the O’Brien empire is for Irish media and society in general. Mr O’Brien may justifiably claim a right to reputation, but the right of the press to report parliamentary proceedings is paramount in a functioning democracy,” Reidy said.

Although he owns up to 20 national and regional newspapers, as well as two major radio stations, O’Brien lives in Malta for tax purposes.